The present invention relates to a holding seal member for covering the peripheral surface of an exhaust gas purifier body housed in a metal shell, an exhaust gas purification apparatus employing the same, a jig for chamfering the holding seal member, and a manufacturing method for the holding seal member.
An exhaust gas treatment apparatus for use in a vehicle is normally located in the middle of an exhaust passage in a vehicle. A diesel particulate filter (DPF) and an exhaust gas purifying catalyst converter, which removes graphite particles referred to as particulates, are known in the prior art as examples of an exhaust gas treatment apparatus. A typical exhaust gas treatment apparatus includes an exhaust gas purifier body, a metal pipe (shell) enclosing the exhaust gas purifier body, and a holding seal member filling the gap between the exhaust gas purifier body and the metal pipe.
The holding seal member must function to prevent the exhaust gas purifier body from being broken when hit against the metal pipe due to vibrations of the vehicle. The holding seal member must also function to prevent the exhaust gas purifier body from falling off from the metal pipe or moving in the metal pipe when subjected to exhaust gas pressure. Further, the holding seal member must prevent the exhaust gas from leaking out of the gap between the metal pipe and the exhaust gas purifier body.
FIG. 1 shows a conventional holding seal member 14p. FIG. 2 shows an exhaust gas treatment apparatus employing the conventional holding seal member 14p. The holding seal member 14p is formed by cutting a fiber mat 16 having uniform thickness and resilience. The holding seal member 14p is wound around the peripheral surface of an exhaust gas purifier body 21. The exhaust gas purifier body 21, around which the holding seal member 14p is wound, is pressed into a metal tubular shell 23. The exhaust gas treatment apparatus is assembled in this manner (refer to JP-A-2001-316965).
The exhaust gas purifier body is, for example, a catalyst carrier. Catalytic activity is dependent on the temperature. The fiber mat must be thermally insulative to ensure sufficient reactivity for the catalyst from an initial state of usage. The material of the fiber mat is, for example, inorganic fibers such as alumina fibers. JP-A-2003-20938 describes a holding seal member having of which heat resistance, holding capacity under high temperatures, and resistance to eolian erosion are all improved. This holding seal member is made from inorganic fibers having an adjusted rate of mullitization.
When the holding seal member 14p and the exhaust gas purifier body 21 are pressed into the shell 23, a shearing force acts on the inner surface 14n and outer surface 14j of the holding seal member 14p so as to deform the holding seal member 14p. As shown in FIG. 3, a projection 14k projects from the deformed holding seal member 14p. The projection 14k has an acute apex between the outer surface 14j and end surface 14d of the holding seal member 14p. The angle of the projection 14k opposing the acute apex faces the direction opposite from the direction in which the holding seal member 14p and the exhaust gas purifier body 21 are pressed.
Even if the holding seal member has improved resistance to eolian erosion, the acute apex of the projection 14k is apt to being eroded by exhaust gas and thus easily breaks. Inorganic fibers released from the broken projection 14k may enter the exhaust gas purifier body 21 and clog the exhaust gas purifier body 21.
Recent improvement in engine performance causes a trend of increasing exhaust gas pressure. Thus, the holding seal member 14p is wrapped around the entire outer peripheral face of the exhaust gas purifier body 21 so as to keep holding the exhaust gas purifier body 21 even under high exhaust gas pressure. This has induced a recent problem in that the projection 14k is easily produced, resulting in clogging of the exhaust gas purifier body.
Further, if the projection 14k is cut after pressing the holding seal member 14p into the shell 23, the exhaust gas purifier body 21 and the shell 23 may be damaged. Therefore, it is not desirable to cut the holding seal member 14p after the holding seal member 14p is pressed into the shell 23.